The role of speed detection in traffic safety enforcement is widespread throughout the United States and the principal tool for police traffic surveillance is Doppler radar. In a police Doppler radar system, an emitted microwave frequency signal is reflected from a target vehicle, causing a change in the frequency of the signal in proportion to a component of the velocity of the target vehicle. The Doppler radar system measures the frequency differential and scales the measurement to miles per hour, for example, in order to display the velocity of the target vehicle to a policeman or other Doppler radar system operator. Using the existing frequency differential scheme, conventional police Doppler radar systems are capable of a high degree of accuracy with regard to vehicle speed measurements in environments having one target vehicle.
Limitations, however, have led to restricting its effectiveness and use in highway-safety programs. Traditional radar devices are not target selective since a beam width of approximately 15° is emitted. As a result, positive operator target identification is perceived as challenging.
Alternative technologies, including Lidar, have been developed and deployed to overcome these limitations. Lidar speed-measuring devices do not operate on Doppler radar principles. Rather, Lidar speed-measuring devices use laser pulses and time-distance principles to measure vehicle speed. The narrow beamwidth, laser pulses of Lidar enable the operator to select individual vehicles and positively identify the target vehicle. But, while Lidar overcomes certain specific limitations associated with radar speed-measurement devices, it introduces challenges of its own. Existing Lidar speed-measuring devices are designed to be aimed and operated from a shoulder, with the butt end of the stock of the device firmly set against the shoulder, or a fixed tripod mount. Both methods make use more cumbersome than that of Doppler radar speed-measuring devices.